Getting back into the hobby again after a hiatus, but I am trying to get my head around how the detachments and formations work in 40K - specifically with the Tau.

There are some great formations in the Farsight Enclaves book, which do not appear in the standard Tau Codex (nor other supplements). I am just wondering if it is possible to use the formations from all of the supplements in one army.

As an example - I am thinking of using creating an army based around:

Retaliation Cadre (Core formation from the Farsight Enclaves)

Counterstrike Cadre (Aux from Farsight Enclaves)

with the Infiltration Cadre (Aux from the Tau Codex).

I am not sure how this works with combined arms etc and would appreciate your thoughts.